In recent years, as image sensing apparatuses using a solid-state image sensing element such as a CCD (Charge Coupled Device) image sensor or CMOS (Complementary Metal Oxide Semiconductor) image sensor increase their performance and reduce the size, cellular phones and PDA (Personal Digital Assistances) with a subminiature digital camera or image sensing apparatus are becoming popular. In addition, demand to mount a zoom lens in these image sensing apparatuses is growing.
In a general zoom lens, all or some of lens groups included in the image sensing lens must be moved. In, e.g., a 3-group zoom lens, lens groups are divided into three groups: a variator group which changes the focal length, a compensator group which corrects focus movement caused by the change in focal length, and a focus group which corrects focus movement caused by the change in object distance, or a variator group, a group having a compensator and focus function, and a fixed group. Of the lens groups, predetermined lens groups are moved in the coaxial direction to execute zooming and focus adjustment. As a detailed example of such a zoom optical system, a zoom lens which executes zooming and focus adjustment by moving two or three groups is disclosed (Japanese Unexamined Patent Publication No. 2002-350726).
As disclosed in Unexamined Patent Publication No. 2002-350726, when a plurality of lens groups are moved in the coaxial direction to execute zooming and focus adjustment, a moving mechanism to move the lens groups is necessary. The moving mechanism is generally complex. In addition, a wide space is necessary to arrange the moving mechanism.
Another zoom lens is known, which decreases the number of moving groups by using a refractive power variable element and imparts, to this element, the focus movement correction function for zooming or a variation in inter-object distance. As a detailed example of such a zoom lens, a zoom lens using a reflection refractive power variable element is also disclosed (Japanese Unexamined Patent Publication No. 2003-98435).
However, when the reflection optical element disclosed in Japanese Unexamined Patent Publication No. 2003-98435 is used, aberration asymmetrical with respect to the co-axis is generated. To correct the aberration, the reflecting surface must be, e.g., a free-form surface which is hard to control.